1. Technical Field
A method for fabricating a semiconductor device is disclosed. In particular, an improved method for fabricating a high speed semiconductor device is disclosed where the device includes a salicide. In the disclosed method, a shallow and a deep source/drain region are formed simultaneously by forming an insulating film spacer on sidewalls of a gate electrode, forming SEG (selective epitaxial growth) layer in the LDD (lightly doped drain) region adjacent to the insulating film spacer, and then performing an ion implanting process.
2. Description of the Related Art
In general, the most important function of a transistor of a semiconductor circuit is a current driving function. A channel width of a metal-oxide-semiconductor field effect transistor (MOSFET) is adjusted in consideration of the current driving function. In the most widely-used MOSFET, an impurity-doped polysilicon layer is used as a gate electrode, and a diffusion region formed by doping an impurity on a semiconductor substrate is used as a source/drain region.
A buried channel is formed in a P-type-semiconductor field effect transistor (PMOSFET) which uses an N+ doped polysilicon gate electrode in a complementary metal-oxide-semiconductor field effect transistor (CMOSFET). Here, because a N-type-semiconductor field effect transistor (NMOSFET) having a channel on its surface and the PMOSFET have different threshold voltages, there are various restrictions in design and fabrication of the device.
That is, in the CMOSFET using a dual gate electrode, the dual gate electrodes are formed by ion-implanting N-type and P-type impurities twice. Therefore, a photolithography process should be performed twice, and this complicates the fabrication process. Accordingly, the device can be easily contaminated due to a wet process, and thus the process yield and reliability thereof are reduced.
In addition, as the sizes of semiconductor devices becomes smaller, the junction depth becomes shallower. However, in high speed devices, large leakage current occurs due to the salicide process in which silicide layers are formed on the source/drain region and the gate electrode.
FIGS. 1A through 1C are cross-sectional diagrams illustrating sequential steps of a conventional method for fabricating a semiconductor device.
First, referring to FIG. 1A, a field oxide 11 defining an active region is formed on a semiconductor substrate 10. A gate oxide 12 and a polysilicon layer (not shown) are formed on the semiconductor substrate 10. Thereafter, the polysilicon layer is etched using a gate electrode mask as an etching mask, to form a gate electrode 13. An LDD region 14 is formed by ion-implanting a low concentration impurity to the semiconductor substrate 10 at both sides of or around the gate electrode 13. An insulating film spacer 15 is formed on side walls of the gate electrode 13.
As shown in FIG. 1B, a first source/drain region 16 is formed by ion-implanting a high concentration impurity to the semiconductor substrate 10 at both sides of or around the insulating film spacer 15. Here, As is ion-implanted for a NMOS, and B11 for a PMOS.
Thereafter, still referring to FIG. 1B, a second source/drain region 17 is formed by implanting a dopant having a high diffusion ratio at a low dose. Here, Ph is ion-implanted instead of As for a NMOS, and B11 instead of BF2 for a PMOS.
As seen in FIG. 1C, a silicide layer 18 is formed on the surfaces of the gate electrode 13, the first source/drain region 16 and the second source/drain region 17.
However, the conventional method for fabricating the semiconductor device has a limit due to shallow junction region resulting from miniaturization of the device. Therefore, increase in the depth of the junction region due to the ion implant process for forming the silicide layer 18 influences the LDD region 14. Especially, when the silicide layer 18 is formed deeply along the rim of the field oxide layer 11, leakage current increases considerably in the junction region of the field oxide 11 and the height of the field oxide 11 is decreased during subsequent processes. In addition, in case of a borderless contact, since the contact is formed along the rim of the field oxide 11, leakage current drastically increases in the junction region of peripheral circuit region.
Accordingly, a method for fabricating a semiconductor device is disclosed which can prevent increase in a junction leakage current and improve a process yield and reliability, by forming a protection film along the rim of the field oxide, forming a SEG layer on the source/drain region, removing the protection film and ion-implanting to form a deep junction in the source/drain region. As a result, the region where the protection film has a deeper junction than the region where the SEG layer is so the ion-implant process has no negative effect on the channel region of CMOS device.
A disclosed method for fabricating a semiconductor device comprises: forming an field oxide defining a active region in a semiconductor substrate; forming a gate oxide and a gate electrode on the active region of the semiconductor substrate; forming an LDD region by ion-implanting low concentration impurities in the semiconductor substrate at both sides of or around the gate electrode; forming an insulating film spacer on each sidewall of the gate electrode; forming a protection film pattern exposing the gate electrode, the insulating film spacer and a portion of the active region of the semiconductor substrate adjacent to the insulating film spacer; forming a SEG layer on the exposed portion of the active region of the semiconductor substrate; removing the protection film pattern; forming a source/drain region comprising a shallow highly dopes source/drain region (xe2x80x9cshallow SID regionxe2x80x9d) and a deep highly doped source/drain region (xe2x80x9cdeep SID regionxe2x80x9d) by ion-implanting high concentration impurities, wherein the shallow SID region is formed beneath the SEG layer and the deep SID region is formed at the exposed active region adjacent to the field oxide where the SEG layer is not formed; forming a silicide layer on the gate electrode, the SEG layer and the active region of the semiconductor substrate.
The protection film pattern may be formed of one or more films selected from a group of silicon oxide film, silicon nitride film, silicon oxynitride film and combinations thereof.
The protection film pattern leaves an exposed portion of the LDD region ranging from about 0.01 to about 1 xcexcm away from the insulating film spacer.
The SEG layer may have a thickness ranging from about 0.01 to about 0.5 xcexcm.
The SEG layer may be a single crystal layer, an amorphous silicon layer or a phosphorous silicon layer.
A novel semiconductor device made in accordance with the disclosed methods is also disclosed.